A conventional drive lock is described in European Patent Application No. 0 642 959. The arrangement derived from such drive lock includes, among other things, an immobilizer which is connected by a data line to an engine control unit. The immobilizer releases the engine control unit for operation only when the immobilizer has received previously determined code signals, and the latter match a stored reference code. Thus, operation of such a vehicle requires a knowledge of the reference code to be entered into the immobilizer. This makes unauthorized operation of the vehicle much more difficult. With some effort it is nevertheless possible to start the vehicle, specifically by replacing the immobilizer by a corresponding unsecured device. To overcome this disadvantage, German Patent Application No. 44 16 644.2 describes corresponding a start of the engine to an exchange of release data between the immobilizer and the engine control unit. In this process, one of the participating devices sends the other a basic code, which it recodes and sends back. At the same time, the sending device generates a recoded code from the basic code in the same way as the receiving device. A release code is generated when the recoded code received back by the receiving device matches the code generated by the transmitting device. With this conventional arrangement, unauthorized starting is impossible even when one of the participating devices is replaced by an unsecured device. However, authorized handling of this arrangement is also made difficult, for example, when one of the devices involved is defective and is to be replaced. Then the used recoding rule must first be determined, but this may take some effort, depending on the system design.
Therefore, the object of the present invention is to provide a drive lock which cannot be bypassed by replacing one of the participating devices and which permits simple handling.